Besides, Kakashi said at one point that he almost can't see with his Sharingan, like no further than half a meter away and yet he watched through his Sharingan only (the other eye was closed), the whole hyper speed combat between Guy and Madara. That fight was happening hundreds of meter away, if not miles at times, so for Kakashi to be able to see it with his Sharingan only, would either suggest a small plot-hole, or that Kakashi is able to regenerate his eyesight to some extend (this would mean that his eyesight worsens only temporarily after using the MS).
On a side note, it's also worth mentioning that Ashura was seemingly able to use all elements (since he uses the senjutsu black balls that are made of them). So he was born with certain bonuses, like Hiruzen and Nagato, indifference to Naruto that needs to depend on the Bijuus for it, as well as a body capable of mastering senjutsu.
Still, Sasuke himself being quite adept at utilizing senjutsu, might eventually lead to him obtaining the full power of So6p, through observation with his new "eye", Naruto's newest Sage Mode.
Also, funny to note, it could be said that Sasuke gained an upgraded MS while Naruto gained an upgraded SM . From the whole beginning MS <=> SM where equal and on opposite side of themselves.